Thesis of Sonda Guermazi

2008 feb.

" Comparative molecular diversity analysis of the microbiome in three municipal anaerobic sludge digesters."
  Sonda Guermazi (mail) supported his thesis on Febrary the 27th in Evry. His research was carried out in the “Cloca maxima” team led by Denis Le Paslier (mail) and Abdelghani Sghir (mail).

  Anaerobic digestion is a natural process, where, under anaerobic conditions, a consortium of microorganisms convert organic matter into methane. The development of culture-independent, mainly PCR-dependant techniques, extended our view of population diversity of this consortium and allowed the discovery of novel bacterial and archaeal lineages. The development of metagenomic approaches allowed a direct access to microbial genomes and permitted to infer their metabolism and their possible functions. In the present work we are analysing and comparing prokaryotic community composition of 3 anaerobic digesters of Corbeil, Creil and Evry treating municipal sludge. Phylogenetic analysis of 16S rDNA sequences show similar profiles for Evry and Corbeil, while Creil is different. Within the bacterial domain, 4 predominant phylogenetic groups are detected : Bacteroidetes, Proteobacteria, Firmicutes and Chloroflexi. However, we observed that some underrepresented bacterial divisions in the anaerobic digesters of Evry and Corbeil, are dominant in Corbeil digester (e.g. Spirochaetales). Within the archaeal domain, we confirm the predominance of Arc I lineage in Evry and Corbeil digesters. No representative of this lineage was found within Creil digester, where Methanosarcinales is the dominant group. The discovery of a novel bacterial candidate division we named WWE3 by a metagenomic approach confirmed that our view of the microbial diversity within these complex ecosystem remains incomplete. To optimise the anaerobic digestion process toward an efficient reduction of sludge, biotic and abiotic parameters should be well handled. Large metagenomic projects will give a glimpse on the metabolic diversity of these ecosystems and will allow us to link metabolism to function. The use of well controlled lab reactors will allow us to understand the microbial process of anaerobic digestion and may permit its optimisation.